Seeds of civilization

When Anthony Ranere dug up the eggplant-sized stones in the Central American tropics in 1973, he knew at once from their blunted edges that someone had used them, over and over again, to pound things to a pulp.

But what was being pounded?

He guessed that the stones were ancient kitchen tools - used to mash edible roots that forest-dwellers had gathered long ago.

Turns out he was only partly right.

In the three decades since then, archaeologists have developed a variety of techniques to determine what was for dinner in the distant past. Often they can distinguish between food that was merely gathered, and food - like the stuff pounded by Ranere's stone tools - that came from plants deliberately grown from seed.

Ranere (pronounced ruh-NEER), a professor in Temple University's anthropology department, is helping to piece together the story of a pivotal moment in human history - the origin of agriculture.

Pivotal, indeed. Food surpluses were accumulated. Permanent settlements were established. Populations grew (and grew), and trade flourished. People took up occupations that had nothing to do with filling their stomachs. And eventually, some grew wealthy and powerful, while others did not.

"All that doesn't happen until people settle down," Ranere says.

Farming was a gradual phenomenon that emerged independently in various locations around the world, enabled by a warming climate more than 10,000 years ago. Ranere, a soft-spoken, bearded fellow who came to Temple in 1973, has made it one of his specialties.

Now 65, his work has taken him from Canada to Pakistan. But it is to the Central American tropics where Ranere journeys time and time again, including return visits to the site in Panama where he found the stone tools 34 years ago. Long before any Europeans had arrived to nickname it the "New World," the experiment of growing food on purpose was well under way in Central and South America - fueling a growth in international trade.

"Things are just moving back and forth like mad," he says of that time.

This year alone, Ranere has coauthored three prominent papers on agriculture in the early Americas, providing new insight into the beginnings of such crops as maize, manioc, arrowroot and chili peppers.

Aided by radiocarbon dating, he and others have pushed back estimates for the origins of farming in some locations by thousands of years.

Ranere began his career in an era when archaeologists who studied ancient food were limited to "macro" evidence - shells, corn cobs and other larger remains that survived because they had been charred in a cooking fire.

Since then, scientists have learned new ways to use an old tool: the microscope - enabling them to identify pollen, grains and other remnants that can persist for thousands of years, even in the muggy tropics.

While Ranere's expertise is in excavating and identifying early stone tools, he modestly deflects the credit to his collaborators who perform the painstaking botanical work.

Among the leading practitioners of this analysis is one of his former Temple graduate students, Dolores Piperno.

A Philadelphia native, she divides her time between the Smithsonian Tropical Research Institute in Panama and the National Museum of Natural History in Washington.

One technique Piperno has helped to develop, since the late 1990s, involves the analysis of minuscule food remnants called starch grains. Smaller than the width of a human hair, they can stay embedded for thousands of years in the tiny pits and crevices of stone tools.

These grains can be removed from the rock with ultrasound and examined under a microscope - revealing key differences between wild and domesticated plants.

When a crop is cultivated for years, people select the best specimens to propagate for the next generation - say, because of their size or ease of harvest. Eventually, the plant starts to look different from its wild counterpart, and is said to be domesticated.

This distinction appears even in the microscopic grains, and can be seen thousands of years later, Piperno says. Some domesticated starch grains are consistently bigger than those of wild plants, for example; others take on a different shape.

Not every type of plant leaves these grains behind. So another tool in Piperno's kit, which she first developed 20 years ago, is the analysis of a botanical remnant called a phytolith.

Phytoliths - from the Greek for "plant" and "stone" - are tiny pieces of silica that form inside a plant, providing stiffness for leaves or stalks. They last long after the rest of the plant has decayed, and, like the starch grains, can be analyzed to distinguish the species from which they came.

Some anthropologists were leery of this analysis when Piperno began publishing it, pieces of it in collaboration with Ranere. Because of fast decay in the wet climate, scant evidence of farming had been found in the tropics previously.

But today, the various lines of microscopic evidence are accepted by the broader research community. In February, for example, Piperno and Ranere were part of an international team that published a paper on chili peppers in Science, the leading U.S. scientific journal.

"It's all coming together now," Ranere says.

The various techniques are powerful, yet the ancient shift they reveal is often subtle. There is a transition period when people are still hunting and gathering some plants, Piperno says, but starting to get much of their sustenance from cultivated crops - even before they've been completely domesticated.

"Do we say they're practicing agriculture?" Piperno asks. "We have to be really careful about these terms that we're using."

By piecing together the evidence from various sites throughout the Americas, Ranere, Piperno and their colleagues are able to construct maps of the international flow of goods - and knowledge.

Maize, for example, is thought to have moved steadily southward after it was domesticated more than 9,000 years ago in what today is Mexico. It showed up in Panama about 7,600 years ago, as seen on the stone tools that Ranere excavated in 1973, then in Colombia and Ecuador soon thereafter. Finally, by about 5,000 years ago, it reached Peru and later Uruguay.

On the other hand, manioc - a starchy, whitish root crop - is thought to have been domesticated in Brazil before it marched steadily northward.

"You don't have farmers moving back and forth," Ranere says. "The crops themselves are being exchanged back and forth among people that are already settled into areas."

More evidence will doubtless emerge, as much of the American tropics remains largely untapped by archaeologists. And perhaps once again, science will discover new techniques to analyze the old evidence. Just as it did with Ranere's stone tools from 1973.